Why do guys still flirt when they have a girlfriend?

According to the research, men flirt for six main reasons: to get sex, to explore what it would be like to be in a relationship, to strengthen a relationship, to try to get something, to increase self-esteem, and, well, to have fun.

Is it OK to flirt with someone who has a girlfriend?

So, in short, its OK to be friendly and maybe even a bit flirtatious if you draw clear boundaries and dont plan to take it further. But its best to discuss this with your partner rather than sneaking around their back. That way, perhaps you could even enjoy some flirtation and other monogamish activity together.